The present invention relates generally to a system for placing and receiving telephone calls through a television receiver, and more particularly relates to a circuit for eliminating perturbations such as picture bounce and jitter when dialing a selected telephone number through the television receiver.
U.S. patent application Ser. No. 109,424, now U.S. Pat. No. 4,338,492, filed Jan. 2, 1980 in the name of Paul Snopko and assigned to the assignee of the present invention, discloses a system for receiving and answering in-coming telephone calls through a television receiver. U.S. patent application Ser. No. 243,010, now U.S. Pat. No. 4,356,509, filed Mar. 12, 1981 in the names of Peter Skerlos, Paul Snopko, Frank Templin and Thomas Zato and also assigned to the assignee of the present invention, extends the former system by disclosing a facility for placing or initiating out-going telephone calls through the television receiver. In particular, the television receiver includes a hand-held remote control transmitter having a numerical key-pad operative in a television mode for effecting channel selection. However, in a telephone mode, the same numerical key-pad is operative for effecting a telephone dialing operation for placing an out-going telephone call through the television receiver.
In the telephone mode, each depression of a key of the numerical key-pad corresponds to the selection of a digit of the selected telephone number and results in a unique multibit code being coupled from the hand-held remote control transmitter to the television receiver. The transmitted multibit codes are decoded by a microprocessor incorporated within the television receiver which generates a corresponding output dialing signal consisting of a plurality of 60 millisecond duration logically high pulses separated by a plurality of logically low 40 millisecond inter-pulse intervals, each transmitted multibit code resulting in the generation of a dialing signal comprising a different number of pulses. Each logically low inter-pulse interval renders a switching transistor of a telephone interface circuit conductive for energizing a relay which, in turn, controls an ON/OFF HOOK switch, the condition of the ON/OFF HOOK switch being monitored by the external telephone network for completing the out-going telephone call.
The switching transistor operating the ON/OFF HOOK switch relay is D.C. biased from a regulated television receiver power supply deriving its input from the horizontal deflection system of the television receiver. The regulated D.C. power supply, as well as the receiver horizontal deflection system, additionally supplies operating voltages to various other parts of the television receiver such as the vertical deflection system. It has been found that, during a dialing-out operation, the load on the television receiver power supply is varied in a pulsating manner by the current pulses drawn through the ON/OFF HOOK switch relay, which load variations are reflected throughout the television receiver in the form of operating voltage variations. These operating voltage variations are particularly noticeable in the vertical deflection system of the television receiver where they cause the display image or picture produced on the viewing screen of the receiver to vertically bounce or jitter at the rate of the dialing signal. This effect is quite annoying and detracts from the overall desirability of the television receiver dialing-out function.
It is therefore a basic object of the present invention to provide an improved circuit for facilitating the placing of out-going telephone calls through a television receiver.
It is a more specific object of the invention to provide a circuit for eliminating picture bounce or jitter when dialing a selected telephone number through a television receiver.